Exhaust nozzle switch responsive to afterburner pressure ratio



D. J. JORDAN 2,677,233 EXHAUST NOZZLE SWITCH RESPONSIVE TO AFTERBURNER PRESSURE RATIO 2 Sheets-Sheet 1 May 4, 1954 Filed June 50, 1949 M J m s w o Q T J SQ m J v w N A N M o D Y B $33 QSNK QENQM QQCL QQ EQSSQ SQ QQ mm mmj ATTORNEY y 4, 1954 D. J. JORDAN 2,677,233

EXHAUST NOZZLE SWITCH RESPONSIVE TO AFTERBURNER PRESSURE RATIO Filed June 50, 1949 2 Sheets-Sheet 2 l 5. /52 1 i ./56 #0 A L38 w DONALD J. JORDAN A TORNEY Patented May 4, 1%54 UNHTED STATES PATENT OFFICE EXHAUST NOZZLE SWITCH RESPONSIVE TO AFTERBURNER PRESSURE RATIO Application June 30, 1949, Serial No. 102,313

2 Claims.

This invention relates to a pressure switch, particularly to a switch adapted to control mechanism for regulating the area of an exhaust or thrust nozzle.

A feature of this invention is a control switch which provides a signal in response to a change in the ratio of three pressures applied across the switch.

An aiterburner is a device at present employed for augmenting the thrust of a turbojet power plant and is mounted downstream of the turbine rotor. The components of an afterburner consist of a diffuser in which the velocity of the gases is decreased to a value suitable for combustion and a chamber where combustion occurs. Also, it is desirable to employ a variable area exhaust nozzle and it is the purpose of this invention to provide a control switch for regulating the area of this exhaust nozzle.

A feature of this invention is a control switch which provides a signal for opening the exhaust nozzle on an afterburner when combustion has been established within the afterburner combustion chamber.

A feature of this invention is a'control switch which provides a signal for closing the exhaust nozzle on afterburner when combustion ceases in the afterburner combustion chamber.

When combustion is established within an aiterburner, the volume of hot gases passing through the exhaust nozzle increases and a large exhaust nozzle area is required. Should combustion in the aiterburner cease due to blowout of the flame, malfunctioning of the equipment or even when it is halted by the power plant operator, a smaller exhaust nozzle area is required to prevent loss of "thrust. The control switch described herein is designed to sense the presence of combustion and to regulate the exhaust nozzle area accordingly.

Combustion within a confined moving gas stream results in a drop in pressure across the combustion region. This pressure drop is associated with the difference in momentum of the air entering and leaving the region in which heat is added and it can be used as an indication of when combustion is occurring within the afterburner. In a typical combustion chamber the pressure change is usually the sum of the pressure drop due to the addition of heat, called the momentum pressure drop, and a change in pressure due to the geometry of the combustion chamber. At dilierent engine speeds, flight speeds and altitudes, the pressure change across a typical combustion chamber varies widely both with and without combustion. A feature of this invention is a control switch which provides automatic compensation for such changes and provides a signal which will indicate whether a mo mentum drop exists due to the addition of heat.

Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention.

In the drawings,

Fig. 1 is a diagrammatic view of the control switch in conjunction with a turbojet having an afterburner and shows the means for regulating the variable area exhaust nozzle on the afterburner.

Fig. 2 is a sectional view of a control switch in conjunction with a turbojet afterburner.

Fig. 3 is a diagrammatic view of the control switch in conjunction with a turbojet afterburner and shows the use of a sonic nozzle with the switch.

Referring to the drawings in detail, in Fig. 1 there is shown a turbojet power plant Ill having an afterburner [2. The turbojet generally is composed of inlet l4. compressor to, combustion chamber l8, turbine 28 and inner fairing 22. The inner fairing is supported within the power plant by means of several struts, one of the struts being indicated at 24. The afterburner generally is composed of diffuser chamber 25, flame holder 28, combustion chamber 38 and tailpipe 32. The tailpipe is provided with eyelids 3 3 and 35 which move together or apart to vary the area of the exhaust or thrust nozzle defined by the eyelids.

Fuel for the after-burner combustion chamber 36 is admitted to the gas stream through fuel nozzles 36 within the trailing edge of the several supporting struts 2 Fuel may be supplied to these nozzles by means oi annular conduit 38 which is connected through conduit to to a source not shown.

Regulation of the area of the exhaust nozzle is accomplished by means of floating cylinder 32. The cylinder itself is attached by shaft M and arm 46 to the upper eyelid 3 A piston 48 is provided within the cylinder and is attached by piston rod so and arm 52 to the lower eyelid 35. Fluid is supplied to opposite sides of the piston 48 by means of conduits 5 3 and 56, conduit 54 being connected to chamber 58, and conduit 56 being connected to chamber 62. Thus, the eyelids are caused to assume a closed position, giving the smallest exhaust nozzle area, when hold is admitted to chamber 62, and the eyelids are caused to assume an open position, giving the maximum exhaust nozzle area when fluid is admitted to chamber 58. Regulation of the fluid supply to these two chambers is described below.

Pressures at three different stations along the path of the gases through the power plant are used by the control switch 56 to sense combustion within the aiterburner and to regulate the exhaust nozzle area accordingly. These stations are indicated at P1 which is the static pressure immediately downstream of the turbine 20, P2 which is the static pressure ahead of the flame holder 28, and P; which is the static pressure on the downstream side of afterburner combustion chamber 39. Pressures P1 and P2 are the reference pressures, the ratio between them being constant. The ratio of P1 to P3 or F2 to P3 varies with combustion within the afterburnei'. The pressure ratio of P1 to P2 and P1 to P3, and also the ratio of the pressure differences P1-P2 and P1-P3 will remain constant as long as the eyelids 34 and 35 are in a closed position and combustion is not occur 'ng within the aiterburner. However, whcn co ustion occurs, P1 and P2 will increase more than P3, resulting in a change in the pressure ra lie.

The control switch 58 is divided into three chambers as shown at 63, ii} and 12. Chambers 68 and 16 are separated by flexible diaphragm "H and chambers i1; and 12 are separated by flexible diaphragm Chamber $38 is connected by line i i to pressure station P2, chamber i6 is connected by line U to pressure station P3, and chamber 12 is connected by passage ES to pressure station P1. Diaphragms H and '53 are connected by a rigid rod 82 which, through actuator 82 attached to the rod and located within chamber 72, moves electrical contact 84, carried by leaf 8%, whenever the diaphragm assembly moves. Movement of the diaphragm assembly to the left closes electrical contacts 85 and 88, and movement of the diaphragm assembly to the right closes electrical contacts 5d and 95. When contacts 8'3 and 83 are closed, a circuit including wires 32 and 9 and double-acting solenoid 96 is completed and the solenoid is energized. This causes piston as within solenoid actuated valve H39, the piston being connected to the solenoid by means of rod E62, to move to the right admitting fluid from iilet conduit I65 to conduit 54 and to chamber causing the eyelid control to open and increase the area of the exhaust nozzle. Closing of contacts 8d and completes a circuit including wires .72 and i9 3- and energizes solenoid 96 so that piston 98 is caused to move to the left. This will admit fluid from inlet conduit I04 to conduit 56 and chamber $2 causing the eyelid control to close and decrease the area of the exhaust nozzle. When fluid is admitted to conduit 5 conduit 56 is vented to drain iifl and when fluid is admitted to conduit 56, conduit 54 is vented to drain 64.

The control switch 56 operates on the following principle; in a confined gas stream the Mach number any point in the stream bears a deflnite relationship to the Mach number at any other point provided no energy is taken from or added to the stream between the points in question. Thus if the Mach number at one point is the Mach number at all other points is fixed, the ratios of any static or total absolute pressures in the stream are fixed. L. the ratio of the absolute pressures is fixed, the ratio of the pressure differences between any points in the stream is also fixed.

Thus, at a constant value of stream Mach number, the forces Will be balanced. If the Mach number is changed or if energy is added or subtracted from the stream between the pressure stations, the forces will be unbalanced. When combustion occurs within the afterburner combustion chamber 30, the pressure balance is disturbed and the ratio of with combustion and the ratio of without combustion so that the switch is balanced when (Pi-P3) (area of diaphragm 13) (Pz-Pa) (area of diaphragm 1!) Fig. 2 illustrates a control switch I08 constructed in accordance with this invention as applied to the diagrammatic form of the turbojet power plant shown in Fig. 1. The pressures which actuate this switch, however, are difiercnt from those employed with the switch of Fig. 1 and serve to illustrate how various combinations or" pressure stations can be used with this switch provided that the ratio of the pressures P1 and P2 is fairly constant. The turbojet unit is shown at it, the unit having an afterburner i2 comprising diffuser chamber 26, flame holder 28 and combustion chamber 39. In this modification, pressure station P1 is the static pressure of the diffuser chamber 26. Pressure station P2 is the static pressure immediately downstream of flame holder 28, and pressure station P3 is the static pressure on the downstream side of afterburner combustion chamber 38.

The control switch 188 is divided into three chambers as shown at H8, H2 and H l. Chambers H0 and H2 are separated by fiem'ble diaphragm H6 and chambers H2 and H2 are separated by flexible diaphragm H8. Chamber H0 is connected by line iZil to pressure station P2, chamber H2 is connected by line in to pressure station P3, and chamber i M is connected by line 2 3 to pressure station P1. Diaphragms l l6 and H8 are connected by a rigid rod I28, the diaphragms being supported between cups on either end of the rod. An actuator I28 is affixed to the left end of the rod I26 within chamber m and moves leaf 38 carrying electrical contact I32 whenever the diaphragm assembly moves. Movement of the diaphragm assembly to the left closes electrical contacts I32 and $36 to complete a circuit which energizes a solenoid and closes the eyelids 3d and 35 in a manner similar to that described in connection with Fig. 1. Movement of the diaphragm assembly to the right closes electrical contact I32 and contact I40 to complete a circuit which opens the eyelids 84 and 35 to decrease the area of the exhaust nozzle.

Leaf E39 is mounted on insulating block Hi l which in turn is attache. to shaft 555 by means of threads Hi9. Shaft E29 a notch, not shown, at its lefthand end so that upon loosening nut H59 the shaft insulating block can be moved to adjust t position of the contact 132 between the con 9 E35 and 255 after the switch 553 assembied. Pin is pro vided to prevent rotation oi the insulated block 144 while the adjustment is being made.

In Fig. 3 another arrangement the control switch as applied to a turbojet having an aiterburner is shown. ployed with the switch.

159 is divided into three at I55, I53 and Chambers separated by flexible phragu- 52 and bers E58 and are e oarated flexible diaphragm E55. is connected by line 50 to pressure station P1 which is the static pressur in the of a sonic nozzle con nected to co .-pressor discharge pressure at M by means of conduit Air flow from this nozzle is conducted back to the compressor inlet F55 by means of conduit H5. Chamber 558 is connected by means or line l'iii to pressur station P2" which is the compressor discharge static pressure. Chamber 589 is connected by means of line 180 to pressure station P3" which is turbine discharge static pressure.

The ratio or" pressure P1" to P2 is always the sonic ratio while the pressure ratio P2" to P3 is the value for the specific engine. The two pressure ratios will remain constant as will the ratio of the pressure differences as long as the eyelids 34 and 35 are in a closed position and there is no combustion within the afterburner. When combustion occurs, pressure P3" will rise and pressure P1 and pressure P2" will be unchanged. Conversely, when combustion ceases, pressure Pa" will drop.

When a change in the ratio of the pressure difrlere a sonic nozzle The r ferences occurs, the diaphragm assembly E82 will I Pz-Pg P P and the other set to close the eyelids at a relatively large increase in this pressure ratio.

Since the control switch has little or no spring rate, it is highly sensitive and can be made to respond accurately to changes in pressure ratio of less than 1 percent at high altitudes.

It is to be understood that the invention is not limited to the embodiments herein illustrated and described but may be used in other ways without departure from the spirit as defined by the claims.

I claim:

1. A jet engine including a compressor, a tute driving said compressor, a combustion chamber receiving compressed air from the compressor and supplying combustion gases to drive said turbine, an aiterburner receiving combustion gases from tuib and compressor and having mounted on its downstree a nozzle through wl oh the combustion gases are discharged, means for varying the area or" said nozzle, and pressure responsive means controlling said noz- Zle are varying means including a housing havth chambers therein defined by interconnected daphragms of different areas, three presstations at spaced points along the gas path through said ai'terburner, one station located adjacent the turbine end of said aiterburner, another station located in the downstream portion oi said aiterburner, the third station located between and spaced from said other stations, and a fluid connection between each of said chambers and one of said stations so that nozzle area is controlled as a function of pressure ratio in said aiterburner.

2. A jet engine including a compressor, a turbine driving said compressor, a combustion chamber receiving compressed air from the compressor and supplying combustion gases to drive said turbine, an aiterburner receiving combustion gases from said turbine and compressor and having mounted on its downstream end a nozzle through which the combustion gases are discharged, said aiterburner including a diiiuser and a flame holder, means for varying the area of said after burner nozzle, and pressure responsive means controlling said nozzle area varying means including a housing having three chambers therein defined by interconnected diaphragms of difierent areas, one chamber having a fluid connection with said difiuser, another with the downstream side of said fiameholder, and the third with the downstream portion or said aiterburner, and a switch connected to and actuated by movement of said interconnected diaphragms to automatically control said nozzle area varying means and adjust nozzle area as a function of pressure ratio in said aiterburner.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,444,163 Kocmich June 29, 1948 2,452,500 Smith Oct. 26, 1948 2,457,595 Orr Dec. 28, 1948 2,483,401 Cole Oct. 4, 1949 2,498,939 Bobier, Jr. Feb. 28, 1950 2,514,248 Lombard July 4, 1950 2,520,957 Schmitt Sept. 5, 1950 2,537,772 Lundquist 1951 2,540,594 Price Feb. 6, 1951 2,545,703 Orr Mar. 20, 1951 2,565,961 Poole Sept. 4, 1951 2,580,962 Sdille Jan, 1, 1952 FOREIGN PATENTS Number Country Date 587,558 Great Britain May 3, 1947 

